A noninvasive estimation of mixed venous oxygen saturation using near-infrared spectroscopy by cerebral oximetry in pediatric cardiac surgery patients

The use of near-infrared spectroscopy during an extubation readiness trial as a predictor of extubation outcome

OBJECTIVES

To determine whether the measurement of cerebral and somatic regional oxygen saturation during an extubation readiness trial predicts extubation failure in postoperative cardiac patients.

DESIGN

Prospective observational study.

SETTING

Tertiary care center cardiac ICU.

PATIENTS

Pediatric patients 1 day to 21 years old following cardiac surgery for congenital heart disease. Patients were included if they were intubated for greater than 12 hours and were undergoing an extubation readiness trial.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Data collection included patient demographic, procedural, laboratory, and physiologic variables. Regional oxygen saturation values were recorded using near-infrared spectroscopy at baseline, during a 2-hour extubation readiness trial, and in the first 2 hours postextubation. Ninety-nine extubation readiness trials were conducted in 79 patients. Adjusting for baseline somatic regional oxygen saturation, logistic regression analysis demonstrated that patients with a decline in their minimum somatic regional oxygen saturation of at least 10% during an extubation readiness trial had a 6-time increased odds of extubation failure (p = 0.02; 95% CI, 1.26-29.8). Receiver-operating characteristic curve analysis demonstrated that a 12% decline in the minimum regional oxygen saturation best predicted extubation failure with 54% sensitivity and 82% specificity.

CONCLUSIONS

A 12% decline in somatic regional oxygen saturation during an extubation readiness trial is associated with an increased risk of extubation failure following a successful extubation readiness trial. The addition of somatic regional oxygen saturation measurements to an extubation readiness trial may improve our ability to predict extubation outcome.

Neonatal brain protection in cardiac surgery and the role of intraoperative neuromonitoring

Improving mortality rates in children undergoing surgery for congenital heart disease has enabled a shift in focus to improving morbidity, particularly with respect to neurological complications. Various factors have been implicated in influencing neurological outcomes. We share our experience in formulating a customized cardiopulmonary bypass (CPB) protocol based on currently available evidence. Theoretical advantages of intraoperative neuromonitoring during CPB, specifically use of near-infrared spectroscopy, will be discussed in the context of methodologies to monitor cerebral perfusion during surgery.

Web-based survey of current trends in hemodynamic monitoring after congenital heart surgery

Strategies for monitoring patients recovering after congenital heart surgery have evolved considerably as technology continues to progress. Monitoring techniques traditionally centered around the comprehensive physical examination have been replaced by a number of revolutionary technologies developed to objectively evaluate various components of the cardiovascular system. Despite scant evidence that these methodologies actually improve outcomes, some have been embraced by clinicians. We developed an Internet survey designed to describe current practices of clinicians who care for patients after congenital heart surgery. There were 162 respondents to our survey with the majority from the United States. The views of cardiologists, intensivists, those dual trained in both cardiology and critical care medicine, and surgeons are all robustly represented in the results. Serial lactate monitoring was the strategy that was utilized most often by respondents (94%), followed by multisite near-infrared spectrometry (NIRS, 67%). There were 78% who utilized the combination of serial lactate and NIRS monitoring. Serial lactate monitoring was the technique that was thought to best represent cardiovascular well-being after heart surgery (40%). The results of this survey suggest that despite the paucity of evidence that clinical outcomes of patients recovering after congenital heart surgery are improved by any of these monitoring techniques, there is almost universal acceptance to monitor patients with serial lactate monitoring, NIRS monitoring, or a combination of these techniques.

Inferior vena cava oxygen saturation monitoring after the Norwood procedure

BACKGROUND

Superior vena cava oxygen saturation monitoring in the early postoperative period after the Norwood procedure (NP) has been associated with improved survival and decreased adverse events (AE). There is no data describing inferior vena cava saturation (Sivo2) monitoring after NP. We sought to investigate the utility of intermittent Sivo2 monitoring after NP and to assess the correlation of Sivo2 with renal near-infrared spectroscopy (rNIRS). We hypothesized failure to achieve Sivo2 greater than 45% within the first 4 hours after NP is predictive of AE, and that rNIRS correlates with Sivo2.

METHODS

A retrospective study of 26 consecutive NP patients who received postoperative management with Sivo2 monitoring according to a strict protocol was conducted. Primary outcome was AE, defined as cardiopulmonary resuscitation, extracorporeal membrane oxygenation, death before discharge, or residual surgical defects.

RESULTS

Ten (38%) patients had one or more AE; mortality was 23%. On admission to the cardiac intensive care unit, patients with AE had lower Sivo2 (45% ± 9.4% versus 62% ± 12.0%; p < 0.001) and lower rNIRS (56 ± 6.5 versus 77 ± 7.2; p < 0.001). At 4 hours, 90% of AE patients had an Sivo2 less than 45% versus 6% of non-AE patients. Both Sivo2 and rNIRS were highly predictive of AE: the area under the receiver-operating characteristic curve was greater than 0.86 and 0.95, respectively. Two hours after admission, an Sivo2 less than 45% predicted AE with a specificity of 93%, a sensitivity of 70%, and a positive predictive value of 82%. The Sivo2 was strongly correlated with rNIRS (r = 0.81).

CONCLUSIONS

Intermittent Sivo2 can be used to guide early postoperative NP management; rNIRS is an accurate continuous, noninvasive surrogate for Sivo2. An Sivo2 of less than 45% in the first 4 hours after the NP is predictive of AE.

[Regional cerebral oxygen saturation as a marker of hemodynamic state following cardiac surgery]

INTRODUCTION

Regional cerebral oxygen saturation (rSO₂) is a measure of the general state of perfusion and oxygenation. We aim to analyze the relationship between this and various hemodynamic and respiratory parameters.

PATIENTS AND METHODS

Forty-three patients, operated on between October 2011 and July 2012, were included in this prospective observational descriptive study. The following parameters were measured: mean arterial pressure, both arterial and central venous oxygen saturation and partial pressures of oxygen and carbon dioxide, and lactate levels. From these parameters, the oxygenation index and the oxygen extraction ratio were calculated. These measurements were studied to evaluate whether rSO₂ correlated significantly with the other parameters.

RESULTS

The average age and weight of the patients were 27.3 months and 9.2 kg, respectively. The rSO₂ correlated positively with both central venous oxygen saturation (r=0.73, P<.01) and mean arterial pressure (r=0.59, P<.01), and negatively with the oxygen extraction ratio (r=-0.7, P<.01). No correlation was found with the respiratory parameters. Concordance analysis established an acceptable Kappa index (> 0.4) between the rSO₂ and central venous oxygen saturation, and between the rSO₂ and oxygen extraction ratio.

CONCLUSIONS

Regional cerebral oxygen saturation correlates well with hemodynamic parameters - mean arterial pressure, venous saturation, and the tissue oxygen extraction. However, it does not correlate with respiratory parameters.

Resuscitation and perioperative management of the high-risk single ventricle patient: first-stage palliation

Infants born with hypoplastic left heart syndrome or other lesions resulting in a single right ventricle face the highest risk of mortality among all forms of congenital heart disease. Before the modern era of surgical palliation, these conditions were universally lethal; recent refinements in surgical technique and perioperative management have translated into dramatic improvements in survival. Nonetheless, these infants remain at a high risk of morbidity and mortality, and an appreciation of single ventricle physiology is fundamental to the care of these high-risk patients. Herein, resuscitation and perioperative management of infants with hypoplastic left heart syndrome are reviewed. Basic neonatal and pediatric life support recommendations are summarized, and perioperative first-stage clinical management strategies are reviewed.

Does treatment of patent ductus arteriosus with cyclooxygenase inhibitors affect neonatal regional tissue oxygenation?

The effect of patent ductus arteriosus (PDA) treatment with cyclooxygenase (COX) inhibitors (indomethacin [INDO] and ibuprofen [IBU]) on regional oxygenation requires further clarification. The authors hypothesized that both INDO and IBU reduce regional tissue oxygenation in preterm neonates with PDA but that the risk is not uniform for different tissues and other factors may contribute. Regional cerebral (rSO(2-C)), renal (rSO(2-R)), and mesenteric (rSO(2-M)) tissue oxygenation measured by near-infrared spectroscopy and peripheral arterial oxygen saturation measured by pulse oximetry were recorded simultaneously before, during, and after treatment with the first dose of INDO or IBU in very preterm-born infants with PDA. Tissue-specific fractional oxygen extraction (FOE) was calculated using the rSO(2-C), rSO(2-R), rSO(2-M), and corresponding SpO(2) measurements. The findings showed a significant reduction in rSO(2-C), rSO(2-R), and rSO(2-M) and an increase in regional FOE after treatment with COX inhibitors in approximately one third of the 38 enrolled infants, which were associated with increased baseline regional tissue oxygen saturation (p < 0.01). However, the infants with posttreatment reduction of tissue oxygenation had significantly lower baseline rSO(2-C) (66.7 ± 8.1 vs 69.7 ± 8.1 %), rSO(2-R) (55.2 ± 10.8 vs 62.7 ± 11.8 %) and especially rSO(2-M) (37.8 ± 11.4 vs 46.7 ± 16.0 %) than the neonates with unchanged or increased tissue oxygenation. The two groups did not differ in terms of the risk for posttreatment reduction in regional tissue oxygenation with respect to either INDO or IBU treatment and their respective blood levels. Treatment of PDA with either INDO or IBU is associated with a 30-40 % risk for a reduction in regional tissue oxygenation, which is more pronounced in mesenteric tissue than in cerebral or renal tissue. Despite the inconsistency, reduction of regional tissue oxygenation in preterm infants with PDA is more likely associated with the administration of INDO than with the administration of IBU.

Cerebral perfusion during cardiopulmonary bypass in children: correlations between near-infrared spectroscopy, temperature, lactate, pump flow, and blood pressure

Near-infrared spectroscopy (NIRS) is a noninvasive modality to monitor regional brain oxygenation (rSO(2) ). In this study, we aimed to investigate the correlation between cerebral rSO(2) and lactate, pump flow, hematocrit, pCO(2) , and mean blood pressure (MBP) during cardiopulmonary bypass (CPB). Between March and September 2011, 50 pediatric patients who underwent congenital heart surgery were enrolled into the study. Ages ranged from 6 days to 168 months (median 14 months). A NIRS sensor (Somanetics 5100B, Troy, MI, USA) was placed on the right forehead of patients. CPB period was divided into five stages: 1-at the beginning of CBP, 2-cooling at 32°C, 3-at final hypothermic temperature, 4-rewarming at 32°C, 5-before weaning from CPB. Data collection included measurements of each parameter at five stages of CPB. Data were analyzed using multivariate analysis within groups and Spearman's correlation to test association between parameters. Lactate levels increased significantly from stage 1 to stage 5 during CPB (P < 0.05). There was no significant correlation between cerebral rSO(2) and MBPs, pump flows, hematocrit, or pCO(2) during CPB. Cerebral rSO(2) levels showed changes between the stages; there was a significant increase during cooling period, compared to stage 1 (P < 0.05). Significant changes during cooling stage did not happen for other parameters. At stage 3, there was a negative correlation between lactate level and MBP. At stage 4, there was no significant change in cerebral rSO(2) levels despite decreased MBP. At the warming stage, low MBPs, but normal rSO(2) values, are observed despite increased pump flows. Increased rSO(2) levels despite insignificant changes at other parameters during the cooling stage of CPB may show that optimal pump flow with adequate intravascular volume may provide effective cerebral perfusion even without changes in MBP. Considering normal rSO(2) values during CPB in this study, it may be speculated that brain protection can be assessed by using NIRS and applying a standard bypass protocol.

Monitoring of regional tissue oxygenation with near-infrared spectroscopy during the early postoperative course after superior cavopulmonary anastomosis

OBJECTIVES

Near-infrared spectroscopy (NIRS) offers continuous non-invasive monitoring of regional tissue oxygenation. We evaluated NIRS monitoring during the postoperative course after superior cavopulmonary anastomosis in patients with hypoplastic left heart syndrome and anatomically related malformations.

METHODS

Cerebral (cSO(2)) and somatic (sSO(2)) tissue oxygenations were recorded for 48 h and compared with routine measures of intensive care monitoring. Changes in parameters in the case of postoperative complications were evaluated.

RESULTS

Data were obtained from 32 patients. Median age at operation was 2.9 (1.5-10.0) months and weight was 5.3 ± 1.0 kg. Postoperative complications occurred in 7 patients (pulmonary artery thrombus n = 4, pneumothorax n = 1, cardiopulmonary resuscitation n = 1 and low-cardiac output n = 1). cSO(2) was 44 ± 14% at the end of the operation and reached its minimum of 40 ± 11% 2 h later (P = 0.018). Overall, cSO(2) was depressed early after surgery and increased from a mean of 42 ± 11% during the first 4 postoperative hours to 57 ± 8% in the last 4 h of the study period (P < 0.001). The sSO(2) decreased from 77 ± 11% during the early postoperative course to 68 ± 9% within the later course (P < 0.001). The cSO(2) correlated with the arterial partial pressure of oxygen (pO(2), r = 0.364, P < 0.001), with the arterial oxygen saturation (SaO(2), r = 0.547, P < 0.001) and with the central venous oxygen saturation providing the strongest correlation (SvO(2), r = 0.686, P < 0.001). Analysis of agreement between cSO(2) and SvO(2) measurements revealed a mean bias of 0.97 with limits of agreement between 19.8 and -17.9%. Inclusion of both cSO(2) and sSO(2) into a linear regression model slightly improved the prediction of SvO(2) from NIRS values (r = 0.706, P < 0.001). The mean values of cSO(2), sSO(2), SaO(2) and SvO(2) during the early postoperative period were lower in patients with complications (cSO(2): 45 ± 9 vs 29 ± 5%, P < 0.001; sSO(2): 80 ± 11 vs 70 ± 6%, P = 0.004; SaO(2): 76 ± 8 vs 66 ± 6%, P = 0.004; SvO(2): 48 ± 14 vs 32 ± 6%, P < 0.001).

CONCLUSIONS

NIRS technology allows inferring the global oxygenation from continuous non-invasive measurements of regional tissue oxygenation. The cSO(2) is lowered in the early postoperative course. Lower cSO(2) values in the early postoperative course may be predictive of postoperative complications.

Change in regional (somatic) near-infrared spectroscopy is not a useful indicator of clinically detectable low cardiac output in children after surgery for congenital heart defects

OBJECTIVE

Near-infrared spectroscopy correlation with low cardiac output has not been validated. Our objective was to determine role of splanchnic and/or renal oxygenation monitoring using near-infrared spectroscopy for detection of low cardiac output in children after surgery for congenital heart defects.

DESIGN

Prospective observational study.

SETTING

Pediatric intensive care unit of a tertiary care teaching hospital.

PATIENTS

Children admitted to the pediatric intensive care unit after surgery for congenital heart defects.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We hypothesized that splanchnic and/or renal hypoxemia detected by near-infrared spectroscopy is a marker of low cardiac output after pediatric cardiac surgery. Patients admitted after cardiac surgery to the pediatric intensive care unit over a 10-month period underwent serial splanchnic and renal near-infrared spectroscopy measurements until extubation. Baseline near-infrared spectroscopy values were recorded in the first postoperative hour. A near-infrared spectroscopy event was a priori defined as ≥20% drop in splanchnic and/or renal oxygen saturation from baseline during any hour of the study. Low cardiac output was defined as metabolic acidosis (pH <7.25, lactate >2 mmol/L, or base excess ≤-5), oliguria (urine output <1 mL/kg/hr), or escalation of inotropic support. Receiver operating characteristic analysis was performed using near-infrared spectroscopy event as a diagnostic test for low cardiac output. Twenty children were enrolled: median age was 5 months; median Risk Adjustment for Congenital Heart Surgery category was 3 (1-6); median bypass and cross-clamp times were 120 mins (45-300 mins) and 88 mins (17-157 mins), respectively. Thirty-one episodes of low cardiac output and 273 near-infrared spectroscopy events were observed in 17 patients. The sensitivity and specificity of a near-infrared spectroscopy event as an indicator of low cardiac output were 48% (30%-66%) and 67% (64%-70%), respectively. On receiver operating characteristic analysis, neither splanchnic nor renal near-infrared spectroscopy event had a significant area under the curve for prediction of low cardiac output (area under the curve: splanchnic 0.45 [95% confidence interval 0.30-0.60], renal 0.51 [95% confidence interval 0.37-0.65]).

CONCLUSIONS

Splanchnic and/or renal hypoxemia as detected by near-infrared spectroscopy may not be an accurate indicator of low cardiac output after surgery for congenital heart defects.

Non-invasive estimation of jugular venous oxygen saturation: a comparison between near infrared spectroscopy and transcutaneous venous oximetry

The ability of practitioners to assess the adequacy of global oxygen delivery is dependent on an accurate measurement of central venous saturation. Traditional techniques require the placement of invasive central venous access devices. This study aimed to compare two non-invasive technologies for the estimation of regional venous saturation (reflectance plethysmography and near infrared spectroscopy [NIRS]), using venous blood gas analysis as gold standard. Forty patients undergoing cardiac surgery were recruited in two groups. In the first group a reflectance pulse oximeter probe was placed on the skin overlying the internal jugular vein. In the second group, a Somanetics INVOS oximeter patch was placed on the skin overlying the internal jugular vein and overlying the ipsilateral cerebral hemisphere. Central venous catheters were placed in all patients. Oxygen saturation estimates from both groups were compared with measured saturation from venous blood. Twenty patients participated in each group.Data were analyzed by the limits of agreement technique suggested by Bland and Altman and by linear regression analysis. In the reflectance plethysmography group, the mean bias was 4.27% and the limits of agreement were 58.3 to -49.8% (r(2) = 0.00, p = 0.98). In the NIRS group the mean biases were 10.8% and 2.0% for the sensors attached over the cerebral hemisphere and over the internal jugular vein, respectively, and the limits of agreement were 33.1 to -11.4 and 19.5 to -15.5% (r(2) = 0.22, 0.28;p = 0.04, 0.03) for the cerebral hemisphere and internal jugular sites, respectively. While transcutaneous regional oximetry and NIRS have both been used to estimate venous and tissue oxygen saturation non-invasively, the correlation between estimates of ScvO(2) and SxvO(2) were statistically significant for near infrared spectroscopy, but not for transcutaneous regional oximetry. Placement of cerebral oximetry patches directly over the internal jugular vein (as opposed to on the forehead) appeared to approximate internal jugular venous saturation better (lower mean bias and tighter limits of agreement), which suggests this modality may with refinement offer the practitioner additional clinically useful information regarding global cerebral oxygen supply and demand matching.

SjO2/SvO2 correlation during pediatric cardiac surgery with cardiopulmonary bypass

OBJECTIVES

To compare the SjO2 (cerebral oxygenation indicator) and SvO2 (cardiac output indicator) during pediatric cardiac surgery with cardiopulmonary bypass (CPB).

METHODS

Retrospective study. Data of SjO2 and SvO2 measured simultaneously at critical time periods during cardiac surgery with CPB were analyzed by the Spearman correlation test and Bland- Altman plot.

RESULTS

Regression analysis of the pooled data showed poor correlation between SjO2 and SvO2 (r²=0.14, P=0.03) and Bland- Altman plot had a high bias (-7.9), indicating independency of the two variables. SjO2<50% (indicative of cerebral ischemia-hypoxia) were observed in 50% of the measurements after rewarming during hypothermic CPB.

CONCLUSIONS

SvO2 is not a good predictor of SjO2 during pediatric cardiac surgery with CPB, and low SjO2 can be undetected measuring SvO2 only.

Hypoplastic left heart syndrome: current considerations and expectations

In the recent era, no congenital heart defect has undergone a more dramatic change in diagnostic approach, management, and outcomes than hypoplastic left heart syndrome (HLHS). During this time, survival to the age of 5 years (including Fontan) has ranged from 50% to 69%, but current expectations are that 70% of newborns born today with HLHS may reach adulthood. Although the 3-stage treatment approach to HLHS is now well founded, there is significant variation among centers. In this white paper, we present the current state of the art in our understanding and treatment of HLHS during the stages of care: 1) pre-Stage I: fetal and neonatal assessment and management; 2) Stage I: perioperative care, interstage monitoring, and management strategies; 3) Stage II: surgeries; 4) Stage III: Fontan surgery; and 5) long-term follow-up. Issues surrounding the genetics of HLHS, developmental outcomes, and quality of life are addressed in addition to the many other considerations for caring for this group of complex patients.

Understanding near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a noninvasive technique that monitors regional tissue oxygenation reflecting perfusion status. Near-infrared spectroscopy has the ability to continuously and simultaneously monitor tissue perfusion in different organ systems at the bedside without interrupting routine care. Research has demonstrated its benefit in monitoring cerebral, intestinal, and renal perfusion to detect potential ischemic episodes. Near-infrared spectroscopy can augment current physiologic monitoring to increase awareness of abnormal perfusion status in the preterm population and potentially reduce risks associated with many diseases that may lead to ischemic injury. This article provides an overview describing NIRS technology and function, its current use in neonatology, and pertinent research findings illustrating its benefit in the neonatal population. Near-infrared spectroscopy may evolve into an important diagnostic and prognostic tool for neonatal treatment and outcome.

Perioperative care of the infant with single ventricle physiology

OPINION STATEMENT

Among patients with congenital heart defects, neonates with single ventricle disease continue to challenge clinicians despite significant improvements in survival over the past 30 years. The cardiac anatomical variants associated with the term "single ventricle" are characterized by severe hypoplasia (or absence) of either ventricle, typically in association with obstruction or atresia of either the pulmonary or systemic outflow tracts. Physiologically, the single ventricle receives both pulmonary and systemic venous blood and ejects simultaneously into the pulmonary and systemic circulations, a pattern commonly referred to as single ventricle physiology. Medical and surgical management strategies, though palliative, are aimed at achieving the optimal balance of systemic blood flow and pulmonary blood flow to maximize oxygen delivery. Patients with single ventricle physiology have a greater risk of dying than those with biventricular circulations and are generally committed to multiple palliative interventions throughout childhood with considerable risk. Surgical intervention in the newborn period involves Norwood Stage I palliation, placement of a systemic-to-pulmonary artery shunt, or banding of the pulmonary artery, depending on the status of the outflow tracts. Heart transplantation is offered as the initial approach in some centers. The management strategy and the actual delivery of care from the time of birth (or at time of diagnosis) through the postoperative period is crucial to optimize the short-term and long-term outcomes. Whereas survival following initial palliation in experienced centers is as high as 95%, emphasis is now appropriately shifting toward the control of in-hospital morbidity and optimizing long-term functional outcome. Centers are continually striving to gather and apply new knowledge related to the underlying anatomical and physiologic problems while seeking to improve decision making and care of the patient with single ventricle physiology.

Neurocognitive monitoring and care during pediatric cardiopulmonary bypass-current and future directions

Neurologic injury in patients with congenital heart disease remains an important source of morbidity and mortality. Advances in surgical repair and perioperative management have resulted in longer life expectancies for these patients. Current practice and research must focus on identifying treatable risk factors for neurocognitive dysfunction, advancing methods for perioperative neuromonitoring, and refining treatment and care of the congenital heart patient with potential neurologic injury. Techniques for neuromonitoring and future directions will be discussed.

Near-infrared spectroscopy as a hemodynamic monitor in critical illness

BACKGROUND

Near-infrared spectroscopy has moved from a research tool to a widely used clinical monitor in the critically ill pediatric patient over the last decade. The physiological and clinical evidence supporting this technology in practice is reviewed here.

METHODOLOGY

A search of MEDLINE and PubMed was conducted to find validation studies, controlled trials, and other reports of near-infrared spectroscopy use in children and adults in the clinical setting. Guidelines published by the American Heart Association, the American Academy of Pediatrics, and the International Liaison Committee on Resuscitation were reviewed including further review of references cited.

RESULTS

The biophysical properties of near-infrared spectroscopy devices allow measurement of capillary-venous oxyhemoglobin saturation in tissues a few centimeters beneath the surface sensor with validated accuracy in neonates, infants, and small patients. The biologic basis for the relationship of capillary-venous oxyhemoglobin saturation to cerebral injury has been described in animal and human studies. Normal ranges for cerebral and somatic capillary-venous oxyhemoglobin saturation have been described for normal newborns and infants and children with congenital heart disease and other disease states. The capillary-venous oxyhemoglobin saturation from both cerebral and somatic regions has been used to estimate mixed venous saturation and to predict biochemical shock, multiorgan dysfunction, and mortality in different populations. The relationship of cerebral capillary-venous oxyhemoglobin saturation to neuroimaging and functional assessment of outcome is limited but ongoing. Although there are numerous conflicting reports in small populations, expert opinion would suggest that special use may exist for near-infrared spectroscopy in patients with complex circulatory anatomy, with extremes of physiology, and in whom extended noninvasive monitoring is useful.

CONCLUSIONS

Class II, level B evidence supports the conclusion that near-infrared spectroscopy offers a favorable risk-benefit profile and can be effective and beneficial as a hemodynamic monitor for the care of critically patients.

Cerebral NIRS as a marker of superior vena cava oxygen saturation in neonates with congenital heart disease

OBJECTIVES

To investigate the correlation between cerebral near-infrared spectroscopy (NIRS) (rSO2c) and superior vena cava venous oxygen saturation (ScvO2) in newborn patients with congenital heart disease (CHD).

BACKGROUND

NIRS is a noninvasive method to monitor hemoglobin oxygen saturation using nonpulsatile oximetry.

METHODS

We retrospectively analyzed perioperative data from 100 newborn patients who underwent cardiac surgery for CHD. rSO2c, ScvO2 from 24 h before to 72 h after surgery were recorded.

RESULTS

rSO2c had a fair correlation with ScvO2 (r 0.37; P <0.001). The relationship between rSO2c and ScvO2 did not change when analyzed between patients with cyanotic or acyanotic CHD. During the preoperative period, rSO2c levels overestimated ScvO2; in the first 18 postoperative hours, rSO2c underestimated ScvO2; after that period, they showed very close trends. Hypocapnia caused rSO2c to underestimate ScvO2; in normocapnic patients, rSO2c-ScvO2 average differences were close to zero; in hypercapnic neonates, rSO2c tended to overestimate ScvO2. The best performance of rSO2c as a surrogate of ScvO2 was found in the venous saturation ranges from 40% to 60% (r 0.3, P: 0.03).

CONCLUSIONS

rSO2c in newborn patients with cyanotic and acyanotic CHD provides a continuous noninvasive information with a fair correlation with ScvO2%: some predictable variables (i.e., time from surgery, carbon dioxide, and venous saturation levels), should guide the operators to adjust rSO2c values in terms of ScvO2. Serial measures of ScvO2 seem recommended to tailor rSO2c information on actual venous saturation percentage.

Initial Single-Center Experience With Levosimendan Infusion for Perioperative Management of Univentricular Heart With Ductal-Dependent Systemic Circulation

The aim of this study was to evaluate the safety and the efficacy of levosimendan, a novel calcium sensitizer agent, on postoperative hemodynamic and metabolic parameters of neonates affected by single ventricle anatomy. Twenty consecutive neonates scheduled for the Norwood procedure with Blalock Taussig shunt were prospectively enrolled. All patients received an infusion of levosimendan at 0.1 μg/kg/min commencing 24 hours before surgery, and the infusion was continued for 48 hours after surgery. No side effects (intolerance to the drug, hypotension, arrhythmias) were shown. A median inotropic score (IS) of 37 was necessary to maintain a mean arterial pressure between 45 and 50 mm Hg at intensive care unit (ICU) admission: IS was significantly reduced after 72 hours ( P < .05). Brain natriuretic peptide values decreased significantly from 1210 to 459 pg/mL in 72 hours ( P < .05). Median SvO2 increased significantly from 38% to 59% during the evaluated period ( P < .05). Cerebral near-infrared spectroscopy values were close to 40% at ICU admission with a significant stable increase to 50% after 12 hours ( P < .05). Median lactate level was 13 mmol/L at ICU admission but showed a trend to a rapid and significant decrease after 12 hours ( P < .05). Median urine output was surprisingly elevated, always remaining between 5.2 and 6.2 mL/kg/h throughout the postoperative period. Survival rate was 85% at 30 days (17/20 patients) and 75% (15/20) at hospital discharge. Levosimendan infusion in a cohort of neonates with univentricular anatomy was safe and potentially beneficial on postoperative hemodynamic and metabolic parameters.

Noninvasive evaluation of splanchnic tissue oxygenation using near-infrared spectroscopy in preterm neonates

BACKGROUND

Diagnosis of necrotizing enterocolitis (NEC) in preterm neonates is challenging. We hypothesized that regional splanchnic oxygen saturation (rsSO₂) measured by near-infrared spectroscopy (NIRS) is a biomarker for mesenteric perfusion.

OBJECTIVE

To evaluate feasibility and safety of continuous rsSO₂ monitoring in preterm infants in the first 14 days of life.

METHODS

Preterm neonates ≤30 weeks' gestation had a NIRS sensor placed in the left paraumbilical region within 48 h of birth. rsSO₂ was recorded every 30 s. Clinical data including pulse oximetry (SaO₂) were recorded. Fractional tissue oxygen extraction (FTOE) was computed as follows: (SaO₂ - rsSO₂) × 100/SaO₂.

RESULTS

Of 21 infants enrolled, 2 were excluded because of skin breakdown and missing data. Daily mean rsSO₂ values decreased over the first 9 days (p < 0.0001) followed by an increase from day 10 (D10) to D14 (p = 0.0061). rsSO(2) was lower and FTOE was higher in infants with feeding intolerance compared to those without feeding intolerance (p = 0.0043). rsSO₂ accounted for ≥99.5% of the variance in FTOE. Two neonates with NEC had persistently low rsSO₂ with loss of variability preceded or followed by very high rsSO₂.

CONCLUSIONS

We have reported feasibility, safety and ranges for rsSO₂ for a small number of preterm infants in the first 2 weeks of life.

Central venous oxygen saturation and blood lactate levels during cardiopulmonary bypass are associated with outcome after pediatric cardiac surgery

INTRODUCTION

Central venous oxygen saturation and blood lactate are different indices of the adequacy of oxygen delivery to the oxygen needs. In pediatric cardiac surgery, lactate level and kinetics during and after cardiopulmonary bypass are associated with outcome variables. The aim of this study was to explore the hypothesis that the lowest central venous oxygen saturation and the peak lactate value during cardiopulmonary bypass, used alone or in combination, may be predictive of major morbidity and mortality in pediatric cardiac surgery.

METHODS

We conducted a retrospective analysis of 256 pediatric (younger than 6 years) patients who had undergone cardiac surgery with continuous monitoring of central venous oxygen saturation and serial measurement of blood lactate.

RESULTS

Peak lactate was significantly increased when the nadir central venous oxygen saturation was < 68%. Both nadir central venous oxygen saturation and peak lactate during cardiopulmonary bypass were independently associated with major morbidity and mortality, with the same accuracy for major morbidity and a higher accuracy of peak lactate for mortality. A combined index (central venous oxygen saturation < 68% and peak lactate > 3 mmol/L) provided the highest sensitivity and specificity for major morbidity, with a positive predictive value of 89%.

CONCLUSIONS

The combination of a continuous monitoring of central venous oxygen saturation and serial measurements of blood lactate during cardiopulmonary bypass may offer a predictive index for major morbidity after cardiac operations in pediatric patients. This study generates the hypothesis that strategies aimed to preserve oxygen delivery during cardiopulmonary bypass may reduce the occurrence of low values of central venous oxygen saturation and elevated lactate levels. Further studies should consider this hypothesis and take into account other time-related factors, such as time of exposure to low values of central venous oxygen saturation and kinetics of lactate formation.

Near infrared spectroscopy (NIRS) should not be standard of care for postoperative management

Neurologic dysfunction is a problem in patients with congenital heart disease. Near infrared spectroscopy (NIRS) may provide a real-time window into cerebral oxygenation. Enthusiasm for NIRS has increased in hopes of reducing neurologic dysfunction. However, potential gains need to be evaluated relative to cost and potential detriment of intervention before routine implementation. Responding to data in ways that seem intuitively beneficial can be risky when the long-term impact is unknown. Many centers, and even entire countries, have adopted NIRS as standard of care. Available data suggest that multimodality monitoring, including NIRS, may be a useful adjunct. However, the current literature on the use of NIRS alone does not demonstrate improvement in neurologic outcome. Data correlating NIRS findings with indirect measures of neurologic outcome or mortality are limited. Although NIRS has promise for measuring regional tissue oxygen saturation, the lack of data demonstrating improved outcomes limits the support for wide-spread implementation.

Cerebral and somatic near-infrared spectroscopy in normal newborns

PURPOSE

Near-infrared spectroscopy has been used increasingly in the pediatric population as a continuous, noninvasive indicator of trends in organ perfusion and oxygenation. We studied healthy newborn babies to establish normal values during rest and feeding.

METHODS

Forty-four term newborns were recruited. Near-infrared spectroscopy probes were placed on the forehead and over the right kidney to record cerebral (rSO(2)C) and renal-somatic (rSO(2)R) regional oxyhemoglobin saturation. Readings were collected continuously for 2 to 8 hours, spanning 1 to 3 feeding episodes.

RESULTS

Data were available on 26 patients, with an average age of 44 +/- 28 hours. The overall average rSO(2)C was 77.9% +/- 8.5%, rSO(2)R was 86.8% +/- 8.1%, and DeltarSO(2)RC (somatic-cerebral rSO(2) difference) was 8.9% +/- 9.4%. During feeding, rSO(2)C was minimally decreased (78.6% +/- 8.4% versus 78.0% +/- 9.0%, P = .023), rSO(2)R did not change (87.0% +/- 8.1% versus 87.3% +/- 8.0%, P = .31), and DeltarSO(2)RC was minimally increased (8.5% +/- 9.5% versus 9.2% +/- 9.1%, P = .014). Over the first 120 hours after birth, average rSO(2)C decreased (P < .01), and rSO(2)R remained relatively unchanged.

CONCLUSIONS

Clinical utility of near-infrared spectroscopy was partly limited by lack of normative data. These data demonstrate that regional oxygen extraction is greater across cerebral than across renal-somatic beds in normal newborns. Healthy newborns do not have clinically significant changes in organ oxygenation with feeding.

Near infrared spectroscopy in children at high risk of low perfusion

PURPOSE OF REVIEW

Tissue oximetry has been suggested as a noninvasive tool to continuously monitor and detect states of low body perfusion. This review summarizes recent developments and available data on the use of near infrared spectroscopy (NIRS) in children at risk for low perfusion.

RECENT FINDINGS

During states of low cardiac output, cerebral blood flow and thus cerebral NIRS may be better preserved than in somatic tissue sites. Consequently, sites other than the frontal cerebral cortex have been investigated for a possible correlation with invasive measures of systemic perfusion and oxygenation (e.g. abdomen, flank, and muscle). The abdominal site seems preferable to the flank site NIRS (kidney region) application. In order to increase the sensitivity, specificity, and positive predictive value of tissue oximetry to detect systemic hypoperfusion, multisite NIRS such as a combination of cerebral and somatic site NIRS has been suggested. NIRS has also been used to assess systemic perfusion in patients undergoing first-stage palliation for hypoplastic left heart syndrome.

SUMMARY

Despite shortcomings in the ability of NIRS technology to accurately reflect validated and directly measured parameters of systemic oxygen delivery and blood flow, NIRS can certainly assist in the detection of low-flow states (low cardiac output). Large, randomized, prospective studies with well defined outcome parameters are still missing and warranted in order to clearly define the role of NIRS in children at risk for low perfusion.

Near-infrared spectroscopy as an index of brain and tissue oxygenation

Continuous real-time monitoring of the adequacy of cerebral perfusion can provide important therapeutic information in a variety of clinical settings. The current clinical availability of several non-invasive near-infrared spectroscopy (NIRS)-based cerebral oximetry devices represents a potentially important development for the detection of cerebral ischaemia. In addition, a number of preliminary studies have reported on the application of cerebral oximetry sensors to other tissue beds including splanchnic, renal, and spinal cord. This review provides a synopsis of the mode of operation, current limitations and confounders, clinical applications, and potential future uses of such NIRS devices.

Near-infrared spectroscopy monitors: a novel tool for patient safety in the intensive care unit

Medication errors due to adverse incidents with medical devices are a significant contributor to the total number of hospital errors. Unfortunately, there may be no warning when a device fails, and caregivers may not have an opportunity to prevent patient harm as a result. An error of unrecognized interruption of infusions of cardiac medications can cause rapid patient deterioration. In the case presented, near-infrared spectroscopy monitoring alerted caregivers to an otherwise clinically silent error with infused cardiac medications in the intensive care unit and permitted recognition and intervention before patient harm occurred.

Controversies of prophylactic hypothermia and the emerging use of brain tissue oxygen tension monitoring and decompressive craniectomy in traumatic brain-injured children

BACKGROUND

Despite being the leading cause of death and disability in the paediatric population, traumatic brain injury (TBI) in this group is largely understudied. Clinical practice within the paediatric intensive care unit (PICU) has been based upon adult guidelines however children are significantly different in terms of mechanism, pathophysiology and consequence of injury.

AIM

To review TBI management in the PICU and gain insight into potential management strategies.

METHOD

To conduct this review, a literature search was conducted using MEDLINE, PUBMED and The Cochrane Library using the following key words; traumatic brain injury; paediatric; hypothermia. There were no date restrictions applied to ensure that past studies, whose principles remain current were not excluded.

RESULTS

Three areas were identified from the literature search and will be discussed against current acknowledged treatment strategies: Prophylactic hypothermia, brain tissue oxygen tension monitoring and decompressive craniectomy.

CONCLUSION

Previous literature has failed to fully address paediatric specific management protocols and we therefore have little evidence-based guidance. This review has shown that there is an emerging and ongoing trend towards paediatric specific TBI research in particular the area of moderate prophylactic hypothermia (MPH).

Definition of hypotension and assessment of hemodynamics in the preterm neonate

The complexity of postnatal cardiovascular transition has only recently been better appreciated in the very low birth weight neonate. As blood pressure in itself poorly represents systemic blood flow, especially when the fetal channels are open and the developmentally regulated vital organ assignment may not have been completed, efforts to measure systemic blood flow have resulted in a novel, yet incomplete, understanding of the principles and clinical relevance of cardiovascular adaptation during postnatal transition in this patient population. This article describes the definition of hypotension based on the principles of cardiovascular physiology, and reviews the tools available to the clinician and researcher at the bedside to examine the complex relationship among blood pressure, systemic and organ blood flow, and tissue oxygen delivery and oxygen demand in vital and non-vital organs in the very low birth weight neonate. Only after gaining an insight into these complex relationships and processes will we be able to design clinical trials of selected treatment modalities targeting relevant patient sub-populations for the management of neonatal cardiovascular compromise. Only clinical trials based on a solid understanding of developmental cardiovascular physiology tailored to the appropriate patient sub-population hold the promise of being effective and practical, and can lead to improvements in both hemodynamic parameters and clinically relevant outcome measures.

Cerebral oxygen saturation monitoring for off-pump coronary bypass graft surgery with Moyamoya disease: A case report

We report a case using cerebral oxygen saturation (rCbO2) for off-pump coronary artery bypass graft (OPCAB) surgery in a patient with co-existing Moyamoya disease. The rCbO2 with the routine monitoring for OPCAB surgery were monitored intraoperatively. In spite of infusing nimodipine (0.2 microgram/kg/min) and maintaining the end-tidal CO2 tension at 35-40 mmHg, a sudden reduction in the right-side rCbO2 from the base line value of 70-80%/78-83% (Left/Right) to 70-72%/65-70% was developed during the harvesting of the vascular graft. We increased the rate of phenylephrine infusion to increase systemic and cerebral perfusion pressure, and both rCbO2 values were elevated to 80%/70% within 3 minutes. However, the preferential reduction in the right-side rCbO2 compared with the left-side value was not corrected. While suspecting cerebral ischemia due to cerebral vascular spasm, we administered nimodipine 2 mg bolus and increased infusion rate to 0.5 microgram/kg/min. Finally, the preferential rCbO2 reduction in the right-side was corrected and both rCbO2 reached 84%/91%. We concluded rCbO2 monitoring is useful for detecting an intraoperative episode of cerebral ischemia and maintaining the optimal cerebral perfusion during OPCAB surgery with Moyamoya disease.

Correlation of cerebral Near-infrared spectroscopy (cNIRS) and neurological markers in critically ill children

OBJECTIVE

To correlate regional brain saturations (RSO(2)) measured by cerebral Near-infrared spectroscopy (cNIRS) with serological markers indicative of neurological injury (neuron-specific enolase (NSE) and S100beta).

METHODS

Children with at least one organ failure who were undergoing cNIRS monitoring were eligible for enrollment, while children with hyperbilirubinemia and cyanotic heart disease were excluded. Children were further analyzed based on the presence of an acute neurological injury (defined as hypoxic/ischemic injury after cardiac arrest, status epilepticus, meningitis, encephalopathy) as well as survival. RSO(2) was measured continuously (every 30 s) and averages were obtained at 6 h and 24 h epochs prior to serum collection (E6 and E24, respectively). Serum was collected for NSE and S100beta, which were both determined by ELISA. Serum from children undergoing evaluation for fever in the Emergency department served as serological controls. Correlations were determined using the Pearson Product Moment Correlations.

RESULTS

A total of 26 children underwent cNIRS monitoring for a total of 47 days. Overall NSE was greater in critically ill children compared to controls, as well as in all subsets of children analyzed (acute CNS injuries, no acute CNS injuries, survivors and non-survivors). S100beta tended to be greater in critically ill children, but this did not reach statistical significance. Average RSO(2) in E6 and E24 was 68.0% +/- 1.5 and 68.6% +/- 1.6, respectively, in a total of 131,036 measurements and E6 RSO(2) was strongly, negatively correlated with S100beta in children with acute neurological injuries.

CONCLUSIONS

This is the first study to correlate averaged RSO(2) measured by cNIRS with neurological injury markers in critically ill children. We believe that this data can be used to establish thresholds for RSO(2) that can be tested in future trials to determine if this technology is predictive of long-term neurological outcome.

Evaluation of cerebral oxygenation during procedural sedation in children using near infrared spectroscopy

STUDY OBJECTIVE

We evaluate the utility of near infrared spectroscopy monitoring and its correlation to conventional respiratory monitors during changes in cardiorespiratory characteristics during pediatric procedural sedation.

METHODS

In this prospective observational study of 100 children, cerebral oxygenation (rSO(2)), pulse oximetry (SpO(2)), and end-tidal carbon dioxide (etco(2)) were monitored continuously. Values were manually recorded at least every 3 minutes from baseline until 30 minutes after sedative administration, resulting in 1,515 triplicate (simultaneous near infrared spectroscopy/etco(2)/SpO(2)) measurements. Correlations between conventional monitoring characteristics (SpO(2) and etco(2)) and rSO(2) were determined, with focus during adverse cardiorespiratory events.

RESULTS

Cerebral oxygenation remained normal in 1,483 of 1,515 measurements (97.9%). rSO(2) decreased significantly during 3 of 13 hypoxic events occurring in 13 patients and during 5 of 17 hypercarbic events occurring in 8 patients, with 15 measurements of greater than 20% decrease from baseline. Cerebral oxygenation increased transiently in 88% of children. During 31 cerebral desaturation recordings, 3 hypoxic recordings (9.3%, always in combination with hypercarbia) and 5 hypercarbic recordings (15.6%) were observed, whereas in 23 (74.2%), cardiorespiratory characteristics were unchanged. There was poor correlation between rSO(2) and both SpO(2) and etco(2), with correlation coefficients of 0.05 (95% confidence interval 0.04 to 0.07) and 0.01 (95% confidence interval -0.01 to 0.02), respectively.

CONCLUSION

Cerebral oxygenation as measured by near infrared spectroscopy demonstrated few significant negative changes during pediatric procedural sedation. Transient cardiorespiratory events seldom altered rSO(2), with hypercarbia having a greater effect than hypoxemia. However, cerebral desaturations frequently occurred without associated cardiorespiratory changes.

Near-infrared spectroscopy in patients with severe sepsis: correlation with invasive hemodynamic measurements

BACKGROUND

Clinicians have begun using near-infrared spectroscopy (NIRS) to monitor tissue perfusion in hemorrhagic shock, as the technique allows continuous noninvasive monitoring of tissue hemoglobin oxygen saturation (StO(2)) and the tissue hemoglobin index (THI). We hypothesized that StO(2) measurements in patients with severe sepsis would be associated with the severity of their illness and would correlate with invasive hemodynamic measurements.

METHODS

We measured mean arterial pressure (MAP), serum lactate concentration, blood hemoglobin concentration, StO(2), and THI in nine healthy volunteers and ten patients with septic shock in a surgical intensive care unit (ICU). Enrolled patients had a pulmonary artery catheter, and had family able to give informed consent. The average Acute Physiology and Chronic Health Evaluation (APACHE) II score at enrollment for the patients was 19 +/- 5 (standard deviation) points. Volunteers and patients were similar with respect to age and sex. To collect NIRS data, we used the InSpectra Tissue Spectrometer, Model 325 (Hutchinson Technology, Inc., Hutchinson, MN). For three consecutive days, we obtained invasive hemodynamic measurements three times daily, simultaneously with NIRS measurements, and metabolic cart measurements once daily.

RESULTS

Patients with severe sepsis had significantly lower thenar muscle StO(2) values (p = 0.031) than healthy volunteers. Near-infrared spectroscopy-derived mixed venous oxygen saturation (NIRSvO(2)) and StO(2) measured from the thenar eminence in patients with severe sepsis correlated with SvO(2) from the pulmonary artery catheter (p < 0.05). In this group of patients, StO(2) did not correlate significantly with lactate concentration, base deficit, or APACHE II score.

CONCLUSIONS

Near-infrared spectroscopic measurements of StO(2) correlated with invasive hemodynamic measurements in patients with severe sepsis but did not correlate with severity of illness. These findings suggest that NIRStO(2) may be a clinically useful measurement in monitoring patients with severe sepsis. Further study of this device in early resuscitation of patients with sepsis is necessary.

Near-infrared spectroscopy correlates with continuous superior vena cava oxygen saturation in pediatric cardiac surgery patients

BACKGROUND

Cerebral regional oxygen saturation (rSO(2)) measured with near-infrared spectroscopy (NIRS) has a well-proven clinical utility. A goal-oriented treatment based on the rSO(2) resulted in a significant reduction in major morbidity and in a shortening of postoperative hospital stay in patients undergoing coronary revascularization. In this study, we have compared the values of superior vena cava saturation (ScvO(2)) continuously measured with a Pediasat catheter and the corresponding NIRS rSO(2) values obtained during cardiac operations in pediatric patients.

METHODS

This was a prospective observational study enrolling fifteen pediatric patients (age: 6 days-7 years) undergoing cardiac operations. ScvO(2) data obtained with the Pediasat during the operation were compared with simultaneously recorded NIRS rSO(2) values.

RESULTS

One hundred and seventeen matched sets of data were obtained during the operation. ScvO(2) continuously measured with the Pediasat was significantly correlated with the corresponding NIRS rSO(2) values. However, there was a constant positive bias (ScvO(2) values were higher than NIRS rSO(2) values) of 5.6%, with a precision of 10.4%. Time-related percentage changes of NIRS rSO(2) were significantly correlated with the corresponding ScvO(2) percentage changes. A decrease in ScvO(2) is predictive for a decrease in rSO(2) with a sensitivity of 73.7% and a specificity of 85.7%.

CONCLUSIONS

The continuous measurement of ScvO(2) values obtained by the Pediasat may provide useful information about the metabolic conditions of the brain during cardiac operations in pediatric patients if considered as percentage changes. Absolute values of ScvO(2) tend to overestimate the correspondent rSO(2) values.

Significant decrease of cerebral oxygen saturation during single-lung ventilation measured using absolute oximetry

BACKGROUND

Single-lung ventilation (SLV) during thoracic surgery causes important cardiopulmonary disturbances. Absolute cerebral oximetry was used to determine the incidence and magnitude of the decrease in cerebral oxygen saturation (Sct(o(2))) in patients undergoing SLV during thoracic surgery.

METHODS

Data were obtained from 20 consecutive patients undergoing thoracic surgery and necessitating SLV of more than 1 h. The FORESIGHTtrade mark (CASMED, USA) absolute oximeter was used to measure left, right, and average absolute Sct(o(2)) every 5 min from the awake state to extubation. Bispectral index and standard monitoring parameters were also recorded every 5 min. Blood gas analysis was performed every 15 min. Data median (IQR) (range) were analysed using repeated-measures anova and Spearman's correlation test, P<0.05.

RESULTS

Patients [median age 65 yr (range 46-75)] showed an absolute Sct(o(2)) of 80% (78, 82) (74-87) in the awake state, which decreased to a minimum Sct(o(2)) value of 63% (57, 65) (53-73) during SLV to recover to an Sct(o(2)) of 71% immediately after extubation. During SLV, all patients had a decrease of more than 15% of the initial Sct(o(2)) and 70% of patients had a decrease of more than 20%. The decrease in Sct(o(2)) was not correlated with any standard clinical parameters, for example, arterial pressure, blood loss, peripheral oxygen saturation, or Pa(o(2)).

CONCLUSIONS

Thoracic surgery with SLV seems to be associated with a significant decrease of Sct(o(2)) in the majority of patients. Parameters such as peripheral oxygen saturation or Po(2) which are used to guide SLV during thoracic surgery are not sufficient to detect significant cerebral oxygen desaturations.